Celecoxib, a COX-2 (cyclooxygenase-2)-selective inhibitor (coxib), is the only NSAID (non-steroidal anti-inflammatory drug) that has been approved for adjuvant treatment of patients with familial adenomatous polyposis. To investigate if the anti-proliferative effect of celecoxib extends to other coxibs, we compared the anti-proliferative potency of all coxibs currently available (celecoxib, rofecoxib, etoricoxib, valdecoxib, lumiracoxib). Additionally, we used methylcelecoxib (DMC), a close structural analogue of celecoxib lacking COX-2-inhibitory activity. Due to the fact that COX-2 inhibition is the main characteristic of these substances (with exception of methylcelecoxib), we conducted all experiments in COX-2-overexpressing (HCA-7) and COX-2-negative (HCT-116) human colon cancer cells, in order to elucidate whether the observed effects after coxib treatment depend on COX-2 inhibition. Cell survival was assessed using the WST proliferation assay. Apoptosis and cell cycle arrest were determined using flow cytometric and Western blot analysis. The in vitro results were confirmed in vivo using the nude mouse model. Among all coxibs tested, only celecoxib and methylcelecoxib decreased cell survival by induction of cell cycle arrest and apoptosis and reduced the growth of tumor xenografts in nude mice. None of the other coxibs (rofecoxib, etoricoxib, valdecoxib, lumiracoxib) produced anti-proliferative effects, indicating the lack of a class effect and of a role for COX-2. Our data emphasize again the outstanding anti-proliferative activity of celecoxib and its close structural analogue methylcelecoxib in colon carcinoma models in vitro and in vivo.